A transparent water-containing lubricant is known as described in U.S. Pat. No. 3,117,929 and Journal of Colloid and Interface Science, Vol. 42, No. 2 (1973). This lubricant is less flamable than the usual oil type lubricant and thus has received increasing attention in recent years.
Conventional water-containing lubricants, however, have disadvantages in that (1) if the water content decreases owing to evaporation, they change in phase from liquid to solid (the form of phase inversion is unsuitable), (2) therefore, even if water is replenished, the original state cannot be recovered (the phase inversion is irreversible), (3) if the temperature rises, they sometimes change into cloudy emulsions (the phase inversion temperature exists), (4) thereafter, even if the temperature is lowered, the original state sometimes cannot be recovered (the phase inversion temperature exists and then the phase inversion is irreversible), and (5) even though the original state is recovered once, if this cycle is repeated, the original state cannot be recovered. Hence they are not suitable for use as lubricating oils to be used in lubricating parts where the temperature changes cyclically and the amount of water changes invariably.